In the field of analytical science, auto-samplers have made a significant impact on the efficiency, speed and reproducibility of sample processing and injection into analytical instrumentation. Despite these benefits there remains a significant challenge on improving the reduction of sample carryover or cross contamination to a level of eliminating it altogether. The elimination of carry over in auto-samplers is essential for the analysis of clinical samples as well as samples that carry a broad dynamic range of analytes, such as blood plasma, where the range in concentration of analytes can be as large as 1010 to 1012 between the least and most abundant proteins.
The problems associated with the risk of sample carry over can be so significant that only a truly disposable injection system will suffice. Where sample injection volumes are small, for e.g. <2 μl, it is possible to limit the aspiration of a sample to the surfaces of the auto-sampler syringe needle and dispose of the needle between samples. To a great extent, disposable polypropylene tips meet this need, but they are not of sufficient rigidity to pierce the sample vial septa nor are they of the correct design to interface with the typical analytical instrument's injection port. Hence, a metal needle is considered necessary.
For samples greater than the internal volume of the needle or disposable tip, the sample inevitably contacts the internal surfaces of the precision analytical syringe barrel and plunger tip. Once this occurs it is essential to wash the syringe rigorously to remove any risk of sample cross contamination. In the field of clinical assays the perceived risk is so high that disposal of each syringe is sometimes preferable, albeit at great expense with presently available analysis systems.
Another issue with current auto-samplers is their relative lack of flexibility. They typically have fixed arrays of syringes arranged in gantry style on a robotic arm or as discrete moveable heads. In general, these auto-samplers are designed to carry out preprogrammed repetitive bulk analysis tasks at standard uniform sample volumes, and are not easily adaptable to rapid interchangeability between tasks. This issue is addressed in one way by the system disclosed in international patent publication WO 2005/124366, in which a multi-axis transport mechanism selectively moves syringe devices among multiple analysis stations at each of which the devices are detached. Each syringe device is a self-contained “smart” sample probe with an inbuilt motor and controller to effect aspiration and/or dispensing operations. This approach is sophisticated in concept and execution but unduly so far many requirements.
The present inventors have realised that it is possible to develop an improved syringe mounting apparatus and analysis system that are capable of addressing both of the above-mentioned deficiencies with present auto-sampler configurations.